Hello,
Firstly, it was not Kosher who ordered your death, the orders came from Genovese/Bruno-Scarfo. After you left their faction back in May, they placed orders on you within the allotted two week period. If a faction places orders on you within two weeks of you leaving the whitelist, they are allowed to activate those orders whenever it is most convenient for them.
While it is possible for factions to act in OOC bad faith by intentionally waiting an extended period of time and using old orders as ammunition later on, that does not appear to be the case here. The reason it took them so long to kill you was because they did not want to create any bad blood with their ally Kosher. They simply waited until you were no longer under Kosher's protection before acting on the orders. Clearly not acting in bad faith and a good RP reason to do it months later down the road.